TRIQUETRORHABDULUS - an Oligocene/Miocene calcareous nannofossil genus
Milena Biolzi, Katharina Perch-Nielsen and Iraida Ramos
Geology Institute ETH, Sonneggstr. 5, CH-8006 Zurich

The genus Triquetrorhabdulus was erected by MARTINI, 1965, for "three-edged rods, with pointed, rounded or truncated ends", T,carinatus was.

designated as the type species for Triquetrorhabdulus, Since then, several
other species have been assigned to Triquetrorhabdulus (Fig,l) and some havebeen removed again, as T.inversus BUKRY & BRAMLETTE, 1969, which was used
to define a new genus, Pseudotriquetrorhabdulus in WISE & CONSTANS, 1976.

Name

T. carinatus

T. rugosus

AuthorMartini 1965

Bramlette &BukryWilcoxon 1967

Characte~Rid~esw

long
1-<(1971

short, wide
1T. sriatus

T. eh a 11 engeri

Muller 1974

Perch-Nielsen
1977

converg. ridges parallel ridges
4-62-5d)
j~~~

zz

0

long, wide
1T. milowii

"-z

45

I I II?

12I

11w

10z

98w

I-- - I7u60I

5-4:::E321025024::JFig. 1.

3--I I III

The species of Triquetrorhabdulus and their ranges. T,martinii

GARTNER, 1967, is not shown since it is considered to be a juniorsynonym of Rhabdothorax serratus (BRru1LETTE & WILCOXON) ROTH, 1970.
During the re-study of the Oligocene/Miocene interval of DSDP Site 356 on

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Sao Paulo Plateau in the south-West Atlantic, counts of T,challengeri,
which was described from this Site, were made, Fig.2 shows the results ofthis effort.

wo;

JEQ)

~0 c ..00
0 ...c.E<t: Ng.~.
Cl~w":,,zw~Q)
Q)

ICO("')

u -u"
0cl1.(")-ci

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Iz "z__, 0"c<t:-o,_:1.(")"'":I1.(")

COz "'zI~o;n..
E

D 5 D P Site 356

0~~t]

V)

3-1,703-2,723-3,623-4,703-5,703-6,703 cc
4-1,704-2,704-3,704-4,704-5,704-6,704 cc
5-1,705-2,775-3,705-4,705-5,705-6,705 cc
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320 0 l lb102b123456cQ)

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102030123456
RidgesFig.2

Abundance of T.challengeri and number of ridges at DSDP Site 356

The abundance of T.challengeri varies greatly in the samples (Fig.2), but noreason for this was evident in these samples with common to abundant, andreasonably well preserved coccoliths,
Counts of number of ridges ( Figs 2a, 2b, 2c ) show a maximum number of
specimens with 3 ridges in all samples. Specimens with 4 and 5 ridges arefound in Cores 6 through 4 (NN 1 & NN 2), they are absent in Core 3 (NN 2).
Forms with two ridges are absent in Core 6, few in Core 4 and constituteabout 1/3 of the specimens in Core 3. Thus the suspected trend from forms
with many ridges in the lowermost Miocene to forms with fewer ridges higher
in the sequence could be confirmed.
Measurements of the length and the width of T,carinatus in Cores 5 and 6,
where T.carinatus is sometimes abundant and very well preserved, have notprovided data to show any evolutionary trend from long to short, or slender

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to wide forms (or the other way round) ,Both the longest specimen (3M x 36p) and the widest specimen (6p x 20p)
were found in sample 356-6-1, 93 cm, Thus extremely long and slender forms
are found together with shorter and inflated ones, In either forms, theends are pointed, as regarded to be characteristic of T,carinatus.
We can only speculate about the origin of Trisuetrorhabdulus and the'relations between the various species assigned to it, The earliest
representativeof the genus seems to be T,carinatus,which is already foundin Oligocene sediments (NP 24), and has no obvious ancestor, T.milowii could
have evolved from T.carinatus by widening during the Oligocene, its oldest
specimens being of this age. We know of no intermediate forms between
T.carinatus or T.milowii with one ridge, and the early form of T,challen9eri
4• (.

with 3-5 ridges. Unfortunately, no search for an ancestor could be made,since upper Oligocene and lowermost Miocene sediments are missing at Site
356 (the only Site where T,challengeri has been found sofar) and T,challengeri
is missing in complete 0/M boundary sections. T,rugosus can be derived fromT.milowii by the latters growth and developement of ribs perpendicular tothe longitudinal main ridge during the Middle Miocene, T,striatus, withconverging ridges, is found much higher in the Miocene and could have
evolved from T.rugosus, no forms inbetween have been found, however,T.rugosus, on the other hand, may have been the ancestor of Amaurolithus,
more precisely A.primus, thus also of Ceratolithus and thus to a Recent
coccolithophorid (PERCH-NIELSEN, 1977:749).

ReferencesBRAMLETTE,M.N. & WILCOXON,J.A.,l967. Middle Tertiary calcareous nannoplanctonof the Cipero section, Trinidad, W.I. Tulane Studies Geol, v,5,n,3,p.93-131,
BUKRY,D.,l971. Cenozoic calcareous nannofossils from the Pacific Ocean. San
Diego Soc. Nat. Hist., Trans. v.l6, n.l4, p, 303-328,
BUKRY,D. & BRAMLETTE,M.N.,l969. Some new and stratigraphically usefulcalcareous nannofossils of the Cenozoic. Tulane Studies in Geol. and Pal,
7/3:131-142, pls 1-3.
GARTNER,S.,l967. Calcareous nannofossils from Neogene of Trinidad, Jamaica
and Gulf of Mexico. Univ, Kansas Paleontol. Contr., 29~1-7, pls 1-10,
MARTINI,E.,l965. Mid-Tertiary calcareous nannoplankton from Pacific Deep-Sea Cores. In WHITTARD,W.F. & BRADSHAW,R. (ed), Submarine Geology andGeophysics, Proc. 17th Symp. Colston Res. Soc., p,393-411, pls 33-37,London (Butterworths).
MULLER,C.,l974. Calcareous nannoplancton Leg 25 (Western Indian Ocean), In:

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SIMPSON, E.S.W., SCHLICH,R. et al., Initial Reports of the DSDP, vol,25,Washington (U.S. Governement Printing Office), p, 579-633,
PERCH-NIELSEN,K.,l977. Albian to Pleistocene calcareous nannofossils fromthe Western South Atlantic, Df~P, Leg 39. In: SUPKO,P,R., PERCH-NIELSEN,
K. et al., Initial Reports of the DSDP vol. 39, Washington (U,S. Govern.
Printing Office), p. 699-824,
ROTH,P.H.,l970. Oligocene calcareous nannoplankton biostratigraphy, Eglog,Geol. Helv. v.63:799-881, pls 1-14, 17 figs.
WISE,S.W. & CONSTANS,R.E.,l976. Mid Eocene planctonic correlations, NorthernItaly-Jamaica, W.I. Trans. Gulf Coast Ass, Geol, Soc. v,26:144-155, 4 pls,
3 tbs.

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